From 336a7b5dd80a2a7b463dc8ede4862425940edeb5 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Thu, 3 Mar 2016 15:26:56 +1100 Subject: powerpc/module: Create a special stub for ftrace_caller() In order to support the new -mprofile-kernel ABI, we need to be able to call from the module back to ftrace_caller() (in the kernel) without using the module's r2. That is because the function in this module which is calling ftrace_caller() may not have setup r2, if it doesn't otherwise need it (ie. it accesses no globals). To make that work we add a new stub which is used for calling ftrace_caller(), which uses the kernel toc instead of the module toc. Reviewed-by: Balbir Singh Reviewed-by: Torsten Duwe Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/module_64.c | 69 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 68 insertions(+), 1 deletion(-) (limited to 'arch/powerpc/kernel/module_64.c') diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index 9629966e614b..76c0963572f5 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -31,6 +31,7 @@ #include #include #include +#include /* FIXME: We don't do .init separately. To do this, we'd need to have a separate r2 value in the init and core section, and stub between @@ -671,10 +672,76 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, } #ifdef CONFIG_DYNAMIC_FTRACE + +#ifdef CC_USING_MPROFILE_KERNEL + +#define PACATOC offsetof(struct paca_struct, kernel_toc) + +/* + * For mprofile-kernel we use a special stub for ftrace_caller() because we + * can't rely on r2 containing this module's TOC when we enter the stub. + * + * That can happen if the function calling us didn't need to use the toc. In + * that case it won't have setup r2, and the r2 value will be either the + * kernel's toc, or possibly another modules toc. + * + * To deal with that this stub uses the kernel toc, which is always accessible + * via the paca (in r13). The target (ftrace_caller()) is responsible for + * saving and restoring the toc before returning. + */ +static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me) +{ + struct ppc64_stub_entry *entry; + unsigned int i, num_stubs; + static u32 stub_insns[] = { + 0xe98d0000 | PACATOC, /* ld r12,PACATOC(r13) */ + 0x3d8c0000, /* addis r12,r12, */ + 0x398c0000, /* addi r12,r12, */ + 0x7d8903a6, /* mtctr r12 */ + 0x4e800420, /* bctr */ + }; + long reladdr; + + num_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*entry); + + /* Find the next available stub entry */ + entry = (void *)sechdrs[me->arch.stubs_section].sh_addr; + for (i = 0; i < num_stubs && stub_func_addr(entry->funcdata); i++, entry++); + + if (i >= num_stubs) { + pr_err("%s: Unable to find a free slot for ftrace stub.\n", me->name); + return 0; + } + + memcpy(entry->jump, stub_insns, sizeof(stub_insns)); + + /* Stub uses address relative to kernel toc (from the paca) */ + reladdr = (unsigned long)ftrace_caller - kernel_toc_addr(); + if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) { + pr_err("%s: Address of ftrace_caller out of range of kernel_toc.\n", me->name); + return 0; + } + + entry->jump[1] |= PPC_HA(reladdr); + entry->jump[2] |= PPC_LO(reladdr); + + /* Eventhough we don't use funcdata in the stub, it's needed elsewhere. */ + entry->funcdata = func_desc((unsigned long)ftrace_caller); + entry->magic = STUB_MAGIC; + + return (unsigned long)entry; +} +#else +static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me) +{ + return stub_for_addr(sechdrs, (unsigned long)ftrace_caller, me); +} +#endif + int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs) { mod->arch.toc = my_r2(sechdrs, mod); - mod->arch.tramp = stub_for_addr(sechdrs, (unsigned long)ftrace_caller, mod); + mod->arch.tramp = create_ftrace_stub(sechdrs, mod); if (!mod->arch.tramp) return -ENOENT; -- cgit